1. Field of the Invention
This invention relates to a push switch and, more particularly, to a so-called interlocking/single-acting type of push switch wherein as a first one out of two knobs is depressed it is locked at a depressed position (a single-acting mode), whereas as a second one is depressed with the first one in the locked state the second knob is locked and concurrently the first knob is unlocked (an interlocking mode).
2. Description of the Prior Art
Japanese Patent Laid-Open No. 61-47027 discloses a switch of the interlocking/single-acting type, which is shown in FIGS. 9 through 20.
In FIGS. 9 through 13, 31 is a casing equipped with fixed terminals 32. 33a and 33b are operating members slidable in the casing 31 for controlling respective movable contacts 34, each having a sector-shaped hole 35 formed in one side surface thereof. 36a and 36b are stopper pins accommodated in the respective sector-shaped holes 35, each being rockable about a supporting point 37 in the direction of the arrow J as shown in FIG. 11. 38a and 38b are springs for returning the respective operating members 33a and 33b. 39 is an interlocking plate having two heart-shaped cam grooves 40a and 40b formed therein with which respective movable ends 41 of the stopper pins 36a and 36b are in contact, and held in receiving portions 42 of the casing 31 such that the interlocking plate 39 can turn about its support shafts 43 provided at either end thereof. 44 is a torsion coil spring for resiliently pressing respective bottom surfaces 45a and 45b of the heart-shaped cam grooves against the respective movable ends 41a and 41b of the stopper pins 36a and 36b, whose working end 46 is supported in a working hole 47 of the interlocking plate 39 with its stationary end 48 in a fixing hole 49 of the casing 31. 50 is a cover for guiding the operating members 33a and 33b and preventing the operating members 33a and 33b and the interlocking plate 39 from falling off from the casing 31, which is secured to the casing 31 by means of convex portions 51 of the casing 31.
The operation of the interlocking type push switch of the foregoing structure will now be described.
The interlocking operation will first be described with reference to FIGS. 13 through 20. FIG. 13 shows a switch unit K in the released state and another switch unit L in the locked state, FIGS. 14 through 16 are sectional views of the portion of the heart-shaped cam groove 40a of the switch unit K, and FIGS. 17 through 19 are sectional views of the identical portion of the switch unit L. Under the illustrated condition, as the switch unit K is depressed, the movable end 41a of the stopper pin 36a of the switch unit K traces the heart-shaped cam groove 40a so that it moves from point M in the direction of the arrow as shown in FIG. 20, and upon reaching face N, the interlocking plate 39 turns about the support shafts 43 as shown in FIG. 15. In response to a turn of the interlocking plate 39, the movable end 41b of the stopper pin 36b of the switch unit L separates from point Q of the heart-shaped cam groove 40b as shown in FIG. 18, so that the switch unit L changes from the locked state shown in FIG. 17 to the released state shown in FIG. 19, that is, the switch unit L is completely released. If the switch unit K is further subjected to the depression operation, the movable end 41a of the stopper pin 36a reaches full-stroke point P. As the depression force is removed, release action is recovered and the switch unit K comes to the locked state at point Q, hence, the interlocking operation between the switch units K and L is completed. Of course, the identical interlocking operation can also be accomplished even when the switch units K and L are reversed in the order of operation.
Now, the self-locking operation will be described with reference to FIGS. 13 through 16 and FIG. 20. FIG. 13 shows the switch unit K in the released state, and FIG. 14 shows the condition in sectional view of the portion of the heart-shaped cam groove 40a in the released state. Incidentally, in this state the movable end 41a of the stopper pin 36a of the switch unit K stands at point M as shown in FIG. 20. As the depression operation is performed under this condition with respect to the switch unit K, the movable end 41a traces the heart-shaped cam groove 40a in the direction of the arrow, so that after passing over point N, the movable end 41a reaches full-stroke point P. If the depression force is removed in this state, the movable end 41a effects tracing in the direction of the arrow and reaches point Q so that the switch unit K comes to the locked state. In this state, if the depression operation is performed again with respect to the switch unit K, the movable end 41a effects tracing in the direction of the arrow and reaches full-stroke point R. Upon removal of the depression force, the movable end 41a effects tracing in the direction of the arrow and returns to point M, and at this moment the switch unit K recovers its initial released state. Of course, the identical self-locking operation can also be accomplished by the switch unit L.
In the foregoing conventional switch, however, since the two heart-shaped cam grooves 40a and 40b are formed in the interlocking plate 39 with a certain spacing left therebetween, the spacing between the operating members 33a and 33b workable in association with the respective cam grooves 40a and 40b is also restricted, so that the applicability of this type of switch is poor. Further, since the interlocking plate 39 is pulled toward the movable ends 41a and 41b of the stopper pins 36a and 36b at a position deviated from the center thereof by the torsion coil spring 44 whose working end 46 is fitted in the working hole 47 of the interlocking plate 39 with the stationary end 48 supported at the fixing hole 49 of the casing 31, both pulling forces acting at the movable ends have a certain correlation therebetween and tend to lose a balance. Where a balance is lost, there is a fear that the push/lock mechanisms will cause malfunction.